This invention relates generally to methods and apparatus for cooling hot bulk material in a cooling bunker and, more particularly, to methods and apparatus wherein hot bulk material is cooled by passing a stream of cooling gas therethrough.
Still more particularly, the present invention concerns a method and apparatus whereby the flow of cooling gas through a cooling bunker for hot bulk materials is regulated and wherein the cooling gas which is heated after passing through the hot bulk material is recooled in a heat exchanger and returned to the cooling bunker through at least two feed lines.
Arrangements are known for dry cooling coke by injecting cooling gas into a cooling bunker by means of an adjustable blower and wherein the blower operation is regulated according to the cooling requirements. Such conventional arrangements, however, are not entirely satisfactory in that the hot bulk material contained within the cooling bunker tends to become segregated according to grain size resulting in a non-uniform cooling thereof. For example, temperature differences in the bulk material discharged from the outlet of the cooling bunker of between 200.degree.-300.degree. are not uncommon. Furthermore, the cooling gas which passes through the hot bulk material is itself heated in a non-uniform manner and exhibits temperature differences of approximately the same order of magnitude as does the hot bulk material. When such heated cooling gas is used to heat a fluid flowing through a heat exchanger, the non-uniform temperature thereof can result in overheating of the heat exchanger fluid or at least in fluctuations in the output of the heat exchanger.
In order to overcome these disadvantages, it has been proposed to admix a cold cooling gas stream with the hot cooling gas stream. However, this is not satisfactory in that mixing losses necessarily occur.
It has also been proposed in order to overcome the problems noted above to render the volume of coke in the cooling bunker more homogeneous through the provision of a forechamber in the cooling bunker, forming the gas distributor with a multipart design and placing one part of the gas distributor in the peripheral zone of the funnel-like discharge opening of the cooling bunker. However, the use of a forechamber is disadvantageous in that an inverted cone-shaped depression is formed in the bulk material above the gas distributor in the region where the red-hot coke is not cooled, the cooling gas being drawn off only in an annular or peripheral zone of the cooling bunker. In other words, the cooling gas flows essentially rectilinearly from the peripheral zone of the discharge funnel to the gas outlet so that the only advantage provided by the arrangement of a peripheral gas distributor is that an additional cooling gas passage through the coke is formed which at most only slightly improves the cooling conditions. A design of a cooling bunker having a gas evolving surface reduces the extent to which an additional gas passage is formed so that the cooling gas will pass uniformly through only a portion of the hot coke.
It is also conventional to utilize conical gas distributors in cooling bunkers for hot bulk materials. In such arrangements, the tip of the conical gas distributor is disposed in the direction in which the bulk material is charged into the bunker. This in turn causes the cooling gas to pass through the bulk material in a direction which approximates that of a parabola branch which extends toward the wall of the bunker, the flow path also resulting from the fact that the fine grain bulk material becomes situated substantially along the axis of the bunker while the coarse grain bulk material moves in areas adjacent to the bunker wall.
This flow distribution results in an inefficient cooling of the fine bulk material and, furthermore, results in hank formation in the bulk material so that uncooled or inefficiently cooled bulk material will discharge from the bunker. Of course, this is particularly undesirable in the case of hot coke coolers since heat clusters will cause coke burnoff and may also result in damage to transport apparatus onto which the still hot coke is deposited.